The invention relates to a movement device having a Stewart platform, in which a movable platform that has platform joints is connected in an articulated manner by at least six rods to a base. The rods have base joints and, at the base, rest in an articulated manner on carriages. The carriages can be displaced in the longitudinal direction of respective rails that are fixed to the base and extend parallel to one another. Each carriage has a dedicated drive, and the carriages can be moved independently of one another.
In particular, the invention relates to a movement device for positioning a model in the three translational and three rotational degrees of freedom relative to the free inflow of a wind tunnel. In this case, the model is held by a strut in a belly-strut or back-strut arrangement, such that the movement device is located outside the wind tunnel measurement section. This ensures that as little disturbance as possible is introduced into the measurement section. On account of the aerodynamic loads acting via the lever arm and the mass forces, the movement device must be optimized with regard to the greatest possible rigidity with the simultaneous limitation of the maximum drive force.
In many conventional wind tunnels, the suspension of a model in the rear-strut, belly-strut or back-strut arrangement is implemented in such a way that the strut for supporting the model is led out of the measurement section and is held by movement mechanisms arranged serially outside the flow.
The model suspension can likewise be carried out on wires, which in turn are held by a mechanism located outside the measurement section, in the manner of a marionette drive. Changing the position and spatial stabilization is then carried out by pulling on the wires counter to the force of gravity. Such mechanisms are not serial.
Furthermore, in order to implement periodic movements in the air stream to determine dynamic derivatives, strut suspensions are known which are constructed serially such that in each case one axis always respectively supports another. In the case of movements in three degrees of freedom, this already leads to a series connection of the large and heavy axis devices for the movements of the pitching, yawing and rolling, for example, of aircraft models. As a result of the serial, mutually independent axis arrangement of the mechanisms, one axis must always absorb the loads of all the axes arranged after it and must be dimensioned appropriately. As a result, volume and weight increase from axis to axis, and the flexibility of movement and the dynamics are highly restricted. In addition, the accuracy of serial arrangements is determined by the accuracies of the individual axes, because of the error propagation law, and is therefore always poorer than in the case of the respective individual axis. In addition, each individual component is constructed individually, so that the expenditure for fabrication and installation is relatively high.
EP 0 868 255 B1 discloses such a generic movement device for a machine tool or a manipulator. The platform to be moved can be moved in space relative to a base in up to three translational and three rotational degrees of freedom.
In the case of at least four carriages that can move independently of one another on parallel rails, in spite of the one-dimensional preferential direction, the movable platform not only can be moved linearly but can also be tilted. In this case, one of the rails is intended to support exactly two carriages.
Stewart platforms of this type have the advantage of great rigidity with low masses to be moved.
In DE 198 40 886 C2, movement device having a parallel structure is disclosed, in which five guide joint chains are driven by rotary motors. A sixth rod is provided independently thereof as a working spindle.
In EP 1 234 632 A1, a machine tool having four degrees of freedom is described, in which rods in parallelogram arrangements are supported on carriages. Two rails are provided, one rail supporting one carriage and the other rail supporting three carriages. Crossing the rods leads to the linkage of degrees of freedom.
In EP 0 868 255 B1, a movement device having three rails is provided in order to move a body in three to six degrees of freedom.
In DE 101 51 631 B4, a movement device having four rails is provided, each of which supports two carriages. The carriages are aligned parallel to one another and are physically opposite each other, so that they cover a rectangle.
The problem with such Stewart platforms is to provide a degree of rigidity which is constant in virtually all movement situations.